Measurement of the nonlinear coefficient of optical fibers using a coherent receiver

We propose a simple method to measure the nonlinear coefficient of optical fibers. A sinusoidal amplitude-modulated optical wave is injected in the fiber under test, and the output signal is detected with a coherent receiver. The latter allows us to measure a particular quantity, which we name the three-wave phase shift, directly proportional to the nonlinear coefficient of the fiber. The method is valid only if nonlinear and dispersion effects are weak, which is easily achievable in practice. We experimentally demonstrate the method with three types of fibers: a standard single-mode fiber, a dispersion-shifted fiber, and a highly nonlinear fiber.